Skiers were on Saturday warned to exercise extreme caution after a series of deadly avalanches across resorts in the Alps claimed seven lives in just two days.

Heavy snowfall and mild temperatures across the region over Christmas have thrilled those heading off to the slopes with the promise of near perfect skiing conditions. But authorities warned that the current conditions are particularly conducive to triggering avalanches.

An avalanche risk of four to five (out of a maximum five) is expected to remain in place for the next few days and skiers and snowboarders have been warned to stick to marked slopes rather than venturing off-piste.

Even on relatively gentle slopes the avalanche risk has in some places been classed as "considerable".

The Alpine Prefecture warned of "a high risk of avalanches occurring spontaneously or triggered by skiers at all resorts in the Alps". Similar warnings were also issued for the French Pyrenees and in resorts in Italy, Switzerland and Austria and came after a series of deadly avalanches on Thursday and Friday which have left six dead.

In the French resort of Courcheval on Friday, a 44-year-old mountain worker and his 11-year old son were hit by a wall of snow as they attempted to reach a chalet refuge. The boy survived but his father, named as Lionel Blanc, an experienced mountain guide, was killed.

In the nearby resort of Serre-Chevalier, a 16-year-old snowboarder died after being buried in snow during an avalanche under the ski lifts. He was airlifted to Grenoble but died in hospital.

French authorities also announced the death in La Plagne, of an 18-year-old from Brittany. He was rescued alive after being buried in an avalanche but died later in hospital.

A 33-year-old man died and a 38-year-old woman, were critically injured in La Clusaz. The woman is fighting for her life in hospital in Annecy.

Their group of five skiers and snowboarders descended outside the marked runs despite warnings and advice for skiers to remain on the pistes.

At Val-Thorens, seven off-piste skiers set off an avalanche and had to be rescued by the emergency services. Three people were buried but all survived. Police are investigating the circumstances of the avalanche.

Authorities are frustrated that skiers and snowboarders are continuing to take unnecessary risks by ignoring warnings.

Gregory Guzzo, director of the Val-Thorens Tourist Office, said: "At Val-Thorens, we have 30 screens throughout the resort indicating the very high avalanche risk and dangers of off-piste skiing. It's distressing to see people continuing to take risks." In Switzerland, where some resorts recorded a metre of snowfall in 24 hours, two skiers died in separate incidents on Thursday.

The first was swept away in the Piz Nir area above St Moritz and the second, a 27-year-old Irishman described as an experienced cross-country skier, died in an avalanche in the Uri region south of Realp.

Another off-piste skier was injured on the Jakobshorn in nearby Davos.

Also on Thursday, a French skier, aged 24, from Annecy, died in the Italian Alps near the resort of Bardonecchia above Turin.

Authorities there believe the avalanche was triggered by other off-piste skiers and media reports claim the police have opened an investigation for manslaughter.

On Wednesday, a 27-year-old Spanish woman from Barcelona was killed by an avalanche as she skied in a resort in Andorra in the Pyrenees.

And, in the run-up to Christmas, a 16-year-old British schoolboy, Cameron Bespolka, died in Austria and his father remains in a serious condition in hospital.

In the latest incident a 16 year-old-boy was killed in a fall while skiing off-piste in the French alpine resort of Saint-Francois-Longchamp.

Rescue workers reported he had probably hit a rock.

The French authorities have not banned off-piste skiing outright, but they advised skiers and snowboarders to stay on marked ski runs.

Forecasters at Meteo France said: "With the strong temperature swings and very strong winds, the evolution of the snow cover is very variable. The utmost caution is advised to skiers and walkers outside the secured areas."

Pascal Scaviner, a forecaster at Meteo Consult, said: "Heavy snowfalls are expected this weekend above 1600 meters, combined with a strong south wind. This highly wet snow is particularly conducive to trigger avalanches. And the snowpack is very unstable."